Karst

Much of Florida’s landscape is composed of “karst” landforms. A karst terrain is a land surface produced by water dissolving the bedrock and is characterized by sinkholes, cavern systems and disappearing streams and springs. The Alafia River watershed is a textbook example of karst topography.

Florida lies atop a platform of sedimentary rocks many thousands of feet thick. In geologic terms, it was formed 25 to 60 million years ago, when the region was underwater.

The platform is composed of the fossilized remains of sea creatures, mostly tiny invertebrates, which died and sank to the ocean floor. Over millions of years, as the geologic ages passed, the shell remains were compacted into layers of whitish carbonate rock known as limestone.

Karst geologic formations are visible near a spring; photo by Richard Gant

In the Ground

Florida’s limestone platform is honeycombed with underground fractures, cavities and tunnels filled with fresh water. This vast subterranean reservoir is called the Floridan aquifer system. The water stored in an aquifer is referred to as groundwater. Scientists estimate that more than a quadrillion gallons of groundwater are contained in the aquifer.

A Cycle

Before it reaches the aquifer, some of the water is stored in the atmosphere as clouds. When water is discharged from the aquifer, it evaporates and condenses, forming new clouds. This cycle of evaporation, condensation (forming clouds), precipitation (rain) and collection (the accumulation of water in rivers, lakes or below the ground in the aquifer) is called the “hydrologic cycle.”

Short and Long

Sometimes rainwater becomes trapped on the surface and evaporates, or it is transpired by plants and trees before it has a chance to seep into the ground. In those case, the cycle might only take a few days to complete. But when it includes groundwater stored in the aquifer, the hydrologic cycle may take many years.